JPS62191803A - Asymmetrical spherical working focusing rod lens - Google Patents

Abstract

PURPOSE:To obtain a high optical coupling efficiency by a simple constitution, by constituting the titled lens so that at least one surface has an asymmetrical spherical surface, so as to be vertical to an optical axis of a focusing rod lens. CONSTITUTION:In order to solve a problem point generated in case of executing an optical coupling between those which are not similar to each other with regard to a shape of a section of alight beam, the intensity of convergence is made different in the vertical and horizontal directions by a simple constitution, and by deforming the shapes of the light beam sections of a light source side and a photodetecting side so as to become similar to each other, the mode matching is improved and the coupling efficiency is improved. For instance, in case of coupling a DH laser (LD) and a single mode optical fiber 2 (SMF), an asymmetrical spherical surface whose radius of curvature is different in the vertical direction and the horizontal direction is worked on an incident surface of a lens, as the simplest shape of an asymmetrical spherical surface working focusing rod lens. When the radius of curvature of the lens in the vertical direction against an active layer of LD is set to 3.58mm, and the radius of curvature of the lens in the horizontal direction is set to 2.23mm, both focused positions coincide at a position of 5.2mm from the lens. The coupling efficiency in this case becomes excellent as 2-3dB.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a rod lens for optical coupling between a light source and a light-receiving side, in which the cross-sectional shapes of light rays are dissimilar to each other.

BACKGROUND ART As an example of optical coupling between a light source and a light receiving side whose cross-sectional shapes of light rays are not similar to each other, for example, coupling between a semiconductor laser (hereinafter referred to as LD) and an optical fiber can be considered. In many cases, the light emitted from the LD is distributed asymmetrically within its plane, and the total radiation angle perpendicular to the active layer of the LD is L
Seal in the active layer of D1. -7"+Hirakomenmei firing thread ~ 1-1μKoshikimatayo. On the other hand, in most optical fibers, the core is a perfect circle and is symmetrical in the plane with respect to the optical axis. It is.

To couple the output light from this LD to an optical fiber,
It is often done to focus light into a small size using a converging rod lens whose input end is processed into a hemispherical shape.

This method uses a light source and a lens.

Since the optical fibers can be spaced apart from each other to some extent, the light source can be easily packaged in an airtight manner, and since the lens is large, the tolerance of the lens is relaxed.

In addition, the input end of the convergent rod lens is processed into a hemispherical shape to increase the NA of the lens and reduce aberrations, making it possible to combine better than when using a convergent rod lens with a flat input end. An improvement in efficiency has been achieved, with a coupling efficiency of 4 to edB.

Problems to be Solved by the Invention In such conventional methods, since the flat output light of the LD is coupled to the circular cross-section fiber while remaining flat, mode matching is difficult to achieve, and there is a limit to the improvement of coupling efficiency. was there.

The present invention has been made in view of the above points, and has a simple configuration that changes the strength of convergence vertically and horizontally and deforms the shapes of the cross sections of the light rays on the light source side and the light receiving side so that they are similar to each other. The purpose is to improve mode matching and improve coupling efficiency.

Means for Solving the Problems The present invention provides a converging rod lens in order to solve the problems that occur when optical coupling is performed between objects whose cross-sectional shapes of light rays are not similar to each other, as in the above-mentioned example. The object of the present invention is to provide an asymmetric spherically processed focusing Rondo lens in which at least one asymmetric spherical surface is processed perpendicularly to the optical axis of the lens.

Function The present invention makes it possible to vary the strength of focusing by asymmetrically processing at least one of the entrance surface or the exit surface of the focusing rod lens into a spherical surface in accordance with the shape of the cross section of a pair of light rays to be optically coupled. This increases the coupling efficiency.

Embodiment As an embodiment of the present invention, coupling of output light between a flat LD and a single mode optical fiber (hereinafter referred to as SMF) will be described.

The LD in this example is a DH laser, and the wavelength of the output light is 1.3
μm, the total radiation angle of the output light from the LD is 10μm when the active diameter is 10μm.
m, N, A, is 8.5°. The refractive index distribution constant of the converging Rondo lens used to combine these two is 0.
4121. The center refractive index is 1.636. The lens length was set to 3 mm in consideration of ease of processing. Also, L
D = inter-lens distance was set to 0.8 mm in consideration of near-end reflection from the lens end face to the LD. Also, Lens F 1
The distance between the four frames was decided to be at least 5 meters apart due to issues such as packaging.

Under the above conditions, an attempt was made to obtain the highest coupling efficiency using the asymmetric spherically processed focusing rod lens of the present invention.

As the simplest form of the asymmetric spherically machined converging rod lens of the present invention, in this example, an asymmetric spherical surface with different radii of curvature in the vertical and horizontal directions was machined on the entrance surface of the lens. First, since the total radiation angle of the output light that spreads in the direction perpendicular to the active layer of the LD is 500, the radius of curvature of the corresponding lens was set to 3.58 mm. At this time, the exit angle of the light from the lens is 0, which is smaller than N, A, of the SMF used, and the focusing position is 6.2 degrees from the lens. On the other hand, since the total radiation period of the output light that spreads in the horizontal direction with respect to the active layer of the LD is 1o0, the radius of curvature of the corresponding lens was set to 2.23 m+. At this time, the angle of light emission from the lens was 1.3°, and the SMF used
N and A are smaller, and the focusing position is 6.2 meters from the lens, which coincides with the vertical focusing position of the LD. The coupling efficiency in this example is 2-3 dB
was achieved.

Note that when a symmetrical spherical surface with a radius of curvature of 3.58 mm was processed as in the conventional case, the coupling efficiency was 4 to sdB. At this time, the focal position of the output light in the horizontal direction with respect to the active layer was 6.38 m, which was 1.2 m apart from the vertical one, making it difficult to achieve mode matching with the fiber with a circular cross section. It is thought that there was a limit to the improvement of coupling efficiency.

1 and 2 show optical coupling between an LD (semiconductor laser) 1 and a fiber 2 using the asymmetric spherically processed focusing rod lens 3 of this embodiment. FIG. 1 shows the case of emitted light in a direction perpendicular to the active layer of the laser, and FIG. 2 shows the case of emitted light in the horizontal direction with respect to the active layer. By using the lens of the present invention, the coupling efficiency was improved by 1 to 4 dB.

In this example, a spherical surface with different radii of curvature in the vertical and horizontal directions was machined on the entrance surface of the focusing rod lens.
The entrance surface is a symmetrical spherical surface, and the exit surface may be machined with spherical surfaces having different radii of curvature.

Note that when processing a spherical surface, there may be any number of central axes of the spherical surface, and the way in which they intersect corresponds to the shape of the pair of objects to be optically coupled.

Note that the radius of curvature of the spherical surface described above is in the case of infinity (
It also includes planes.

In the embodiment, the coupling of an LD and an optical fiber was described as an example, but any combination may be used, such as an LD and an optical waveguide, an LD and an optical fiber array, an optical fiber and an optical fiber array, etc. This can be applied to optical coupling between a light source and a light receiving side whose shapes are not similar to each other.

Effects of the Invention As described above, according to the present invention, high coupling efficiency can be achieved with an extremely simple configuration, and optical coupling that is extremely useful in practice becomes possible.

[Brief explanation of drawings]

1 and 2 are cross-sectional views showing how an LD and an optical fiber are coupled in an embodiment of the present invention. FIG. 3 is a diagram showing a case where light is emitted in a horizontal direction with respect to the active layer. 1...Semiconductor laser, 2...Single mode fiber, 3...Asymmetric spherical processing focusing rod lens.

Claims (1)

[Claims] An asymmetric spherically processed focusing rod lens, characterized in that at least one surface has an asymmetric spherical surface perpendicular to the optical axis of the focusing rod lens.